SD is a chronic debilitating condition, characterized by selective loss of voluntary voice control during speech production due to uncontrolled spasms in the laryngeal muscles. SD becomes even more incapacitating when it is associated with action-induced voice tremor (VT) due to its poor response to gold standard treatment with botulinum toxin. There is, therefore, a critical need to identify new treatment opportunities for SD/VT patients who receive limited, if any, benefits from botulinum toxin injections. The design and use of novel therapeutic approaches for these patients will, however, be largely unattainable if the central mechanisms of SD and VT development remain unknown. Our long-term goal is to determine the pathophysiology of SD and related disorders, such as VT, for the development of new diagnostic and treatment options for these patients. The objective of this application is to identify brain abnormalities in SD and SD/VT patients as the basis for characterization of central mechanisms underlying symptom improvement following the use of sodium oxybate, a novel pharmacological agent for treatment of ethanol-responsive dystonia. Our central hypothesis is that, compared to SD patients, SD/VT patients will have additional brain abnormalities within the sensorimotor brain circuits controlling voice production, which are being modulated to a greater extent with sodium oxybate treatment. We further postulate that clinical efficacy of sodium oxybate treatment will correlate with its central modulatory effects. The rationale for the proposed research is that identification of distinct brain mechanisms underlying SD and SD/VT clinical manifestations would provide the necessary insights into the pathophysiology of these disorders, while understanding the neural correlates of sodium oxybate action would allow establishment of a scientific rationale for the use of a novel treatment in these disorders. Using a comprehensive approach of multi-modal neuroimaging and clinico-behavioral testing, our central hypothesis will be tested by pursuing two specific aims: (1) determine disorder-specific brain abnormalities in SD and SD/VT patients, and (2) characterize the central effects of sodium oxybate treatment in ethanol-responsive SD and SD/VT patients. This research is innovative because it focuses not only on identification of distinct pathophysiological factors contributing to SD and VT development, but also on discovery of mechanisms of central effects of a novel oral medication, sodium oxybate, which holds promise for treatment of refractory symptoms in SD and SD/VT. The proposed research is significant because it will advance our understanding of the pathophysiology of dystonia in general and SD in particular as well as will have direct impact on improvement of clinical management of SD and SD/VT patients.